Mason bees are very adaptable and tenacious in their push to reproduce. Mason bees succeed best in nest tunnels that measure between 5/16” and 3/8” in diameter; with a tunnel length of 5" to 7". But they (and we) use bigger diameter and shorter - or even longer - lengths. Because of their adaptability, most of the many different types of housing available works if properly used. That said, some are better than others, and this paper discusses their response to all these types.
Since 1995 we have tested multiple different nest systems (the housing is usually called “nests” or “nest systems”), and in this paper nine systems are discussed below. Of them we
primarily use three - newspaper tubes, lined with plain paper;
hollow plant stems cut to length; or grooved wooden boards.
Solitary bees such as Mason bees don’t clean out old debris from the previous year, and so each year they need clean housing. As solitary bees, no-one directs traffic - each bee must find her nest on her own. Large artificial systems with too much uniformity can confuse solitary bees: some asymmetry and bold decorations can help individuals find their nests.

WEATHER PROTECTION

Most nest systems need weather-resistant housing - a large diameter pipe capped at one end; a tennis ball tube; a milk carton set in an open wooden box; some other variation. To reduce rain soaking the nests, tilt the nests a bit forward after first binding them together, (with masking tape, t. p. tubes, et cetera). Shelter from strong wind is also important. In summer or fall move the filled nests into unheated storage - an outside shed, a carport, or the like.

THE SYSTEMS

Newspaper nest tunnels, occupied.

Newspaper tubes with paper liner, (homemade)
• Healthy, inexpensive, disposable, easy to inspect; pest resistant. They take some time to make, but reduce time spent on sanitation and storage. The newspaper helps date them. You MUST line the tubes with ink-free paper and in use they MUST be kept dry.

I roll two different diameters and vary the lengths to make it easier for the bees to locate their nests. With practice, a bundle of 32 tubes takes about ninety minutes to make.

Hollow plant stems
• Plant stems are fun, “natural”, and easy to use if you find the right plants. These are great for education. Mark each year's stems differently to track them. and then discard the old ones. Thin- walled stems are more vulnerable to pests.

Mason bees nests inside hollow plant stems.

Any plant which has a hollow stem at least 5/16” (8 mm) and up to 7/16" inside diameter probably will work; other bees will use smaller diameter stems. The "right" plants are typically weedy ones that grow tall fast. If you are uncertain, use a few the first year and inspect them in the fall. Stems bigger than 5/16” in diameter work fine: bees pack a fat stem with extra cells. I have experimented with several species of plants and routinely inspect the stems of tall thin plants for possibilities.

Wood tray filled (mostly) with cocoons.

Grooved boards - wood

• Grooved wood boards (“trays”) are expensive to start with, but a very good reusable system if you are willing to free and clean all the cocoons; if you are a good woodworker you can make the trays yourself. The trays stack together and resemble drilled blocks. Bees like wood, and the cocoons are usually very healthy. Small parasites - pollen mites and chalcid wasps - may move between nest tunnels when the boards don't mesh perfectly.

"Binderboard" by Pollinator Paradise.

To release cocoons, separate boards and use a chisel-shaped dowel or a dull pencil to free the cocoons, and then clean cocoons as described below. It is best to wash trays too, in warm water with a follow-up dip in bleach water or other disinfectant. Wood trays can also be sterilized in a low temp oven.

Plastic trays opened to reveal cocoons.

Grooved boards - plastic
• Plastic trays superficially resemble wooden ones. They are less expensive and fairly durable. However, given a choice, bees seem to prefer other types of housing. Mud does not stick well to the plastic walls, and plastic does not breath, so humidity can build up. Bees in plastic will be o.k if you free the cocoons by end of October; if left in the plastic blocks until spring, mold and other wet season problems crop up.

Cardboard tubes w/o liner straws
• These are 5/16” diameter cardboard tubes; mason bees do well in them. Good management requires you to somehow date them, as they should only be used once. They are hard to inspect and a bit spendy.

Cardboard tubes w/ liner straws
• Paper liners make cardboard tubes more thrifty and more work. You can buy straws or make your own. Pull the straws each year, (easier said than done), and overwinter them safe from pests. The cardboard tubes you refit with new straws.

Drilled wood blocks (w/ or w/o liner straws)
• Drilled blocks are hard to clean and impossible to open, but if you have untreated scrap wood - lumber or small logs - that every year you drill out as new blocks, they are still a pretty good choice. Holes drilled into 4x4's are shallow and more male bees will be produced; Thicker blocks allow for deeper holes and the deeper, less vulnerable, section of the holes will be laid with female eggs.
Some people use paper liners (see above) to ease inspection and cleaning.

Plastic straws
• Plastic straws I don’t recommend at all except for small experiments and demonstrations. Unfortunately they are marketed by at least one company as a suitable system: I doubt they are.

Shingles and siding

Mason bee built mud nests in a (metal) emergence tray.

• Mason bees are versatile, will nest anywhere, including under shingles, siding, shutters, tree bark, etc. More work for them, but they’ll do it anyway. They may be described as a “pest” in some old literature because of this ability.

Mason bees can make a nest with no tunnel at all, as can be seen in the photo of mud nests built in an emergence tray, (right). The tray is a drawer in a wood box with one emergence hole at the top of the drawer; the closed tray can be seen in the photo of the "BinderBoard", (above). At the time these nests were built, there were other next sites available nearby.

Another example of their adaptability can be seen in a photo of a cluster of cells built by a determined female. She built her nest of cells between two layers of loosely rolled tar paper that I had standing in an outside shed. Reproductively it is not outstanding, as careful examination shows small exit holes in several cocoons from very small parasitic chalcid wasps (Monodontodermus sp.) as well as a moth larva roaming free, (the brown grub in the photo (by the yellow pollen) is NOT a bee larva; bee larvae are white).

--------------

INSPECTING AND CLEANING COCOONS

It is a matter of debate
(and marketing) as to whether or not one needs to clean and wash ALL
the cocoons. I don’t. But only bad pollen allergies and drilled block
systems should stop you from inspecting a few nests, to get an idea of
success and failure. The freed cocoons you then wash and store as
below.
Fall is the best time to inspect nests and wash
cocoons. Opening nests is messy, so be prepared. Some systems are
easy to open, others not so. Inside you will find a line of cocoons,
coated with frass (fecal pellets) and separated by slivers of mud; each
cocoon should hold a dormant adult bee.
A few cells (the
chambers between the mud walls) will be bad. Some cells will be filled
not by a cocoon but instead with a puffy material, which on close look
is pollen teeming with pollen-eating mites. Or, a cell may hold a
mummified larvae. Or, a cocoon may appear fine but be parasitized;
once the cocoons are clean, you can try to cull out the parasites, as
described below.
Open the nests and collect the cocoons in
a bowl or coarse sieve. Once you have released all the cocoons you
intend to wash, sieve out loose debris and pour the cocoons into a
basin of cool water. The cocoons are waterproof and float
while much of the debris washes off and settles. Swirl them around,
drain them, then give them one to three more washings, until the
cocoons seem fairly free of mud, frass, and mites. After the last
rinsing, which some recommend done with a bit of sanitizing bleach, lay the washed cocoons on toweling to dry.
Now
backlight the clean dry cocoons. Most of the cocoons will have a
subtle dark wash - they are black adult bees; a few will be lighter
toned, these pale ones hold parasitic wasp larvae.
One end of
each cocoon is rounded, one end pointed; the pointed “nipple” end
covers the bee’s head. You can open a suspect cocoon with some fine
fingernail scissors, starting at the nipple end. If you find a bee in
the cocoon, recap it with half of an empty cocoon, or just put the open
cocoon in with the other loose ones; the bee will be fine.
Over-winter the washed cocoons loose, on a paper towel in a lidded container, or in an emergence box such as sold by “Pollinator Paradise” or “Beediverse”. Pour the cocoons into the container, not more than two or three cocoons deep,
and put into winter storage with any other nests. If you keep the cocoons in the fridge, close the container with a bit of moisture to compensate for the drying effect of the fridge, and open once or twice a month, (the bees are alive, breathing). In early spring set the container of cocoons out with the nest boxes, (open an emergence hole if you haven't).

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